1. Field of the Invention
The present invention relates to a control system for an outboard motor.
2. Description of the Related Art
There are conventional watercrafts in which a plurality of outboard motors are installed on a stern of the watercraft and the outboard motors are coupled together with a rod-shaped device called a tie bar. In such a watercraft, steering angles of the outboard motors are changed in a coordinated manner. Thus, when the steering angle of the outboard motors is changed, the outboard motors are steered such that a prescribed distance is maintained between the outboard motors. In this manner, a situation in which outboard motors are oriented in different directions from each other does not occur.
Conversely, Laid-open Japanese Patent Application Publication No. 2007-083795 and Laid-open Japanese Patent Application Publication No. 2006-199189 disclose watercrafts in which a plurality of outboard motors are not coupled with a tie bar and, instead, steering angles of the outboard motors are controlled individually. More specifically, in the watercraft disclosed in Laid-open Japanese Patent Application Publication No. 2007-083795, the steering angles of the outboard motors are set according to a traveling performance mode selected by a helmsperson. In the watercraft disclosed in Laid-open Japanese Patent Application Publication No. 2006-199189, target steering angles for a port-side outboard motor and a starboard-side outboard motor are set individually based on a rotation angle of a steering wheel and an engine rotational speed.
In watercrafts such as these, in which a plurality of outboard motors are not coupled with a tie bar, it is possible for a condition to occur in which the steering angles of the outboard motors are greatly different. In such a case, it is possible for one outboard motor to become too close to an adjacent outboard motor such that the outboard motors collide with each other. Laid-open Japanese Patent Application Publication No. 2010-143322 discloses a watercraft in which target steering angles of a plurality of outboard motors are controlled individually such that the steering angle of an outboard motor is larger the farther downstream the outboard motor is positioned in a steering direction. In this manner, a collision between outboard motors is prevented in a watercraft equipped with a plurality of outboard motors not coupled with a tie bar.
Even if the target steering angles are set to angles at which the outboard motors will not collide with each other, there is a possibility that portions of the outboard motors (for instance, their protection covers or their propellers) will collide with each other during a steering operation of the outboard motors. There are times when, for example, a portion of the outboard motors will be replaced with new outboard motors due to a breakdown or other trouble. In such a case, it is possible for the amount of friction occurring in a steering apparatus of a new outboard motor to be different from the amount of friction occurring in the steering apparatus of the original outboard motor. There is a possibility that such a difference in the amount of friction will cause a difference in an engine angular displacement speed of an outboard motor, which is a speed at which the outboard motor is rotated around its steering axis, and result in a collision between the outboard motors. Also, since a state in which the steering angles of the outboard motors differ greatly occurs, there is a possibility that a steering performance of the watercraft will decline.
Additionally, when a difference of the engine angular displacement speed occurs between the outboard motors, there is a possibility that the outboard motors will become greatly separated from each other instead of colliding in the manner explained above. In a case of separation, too, since a state in which the steering angles of the outboard motors differ greatly occurs, there is a possibility that a steering performance of the watercraft will decline.